There is often a building code requirement about room in front of both the toilet to an obstruction and a sink. At 20", I don't think you would meet either clearance requirement in some places. For the toilet, the most common code requires 15" either side of center for a toilet (i.e., a minimum of 30", which you could meet). Now, with a wall-hung sink, you might get by because your knees would likely fit underneath it, but standing back up again might be messy!
You need to find out what the minimum clearances are for Toronto, then that would guide you as to what would be allowable.